The FDA has approved an injectable solution of botulinum toxin type B (Myobloc; Elan Corp, Dublin, Ireland), the first drug to reduce the severity of neck and shoulder muscle contractions and the resulting abnormal head position and neck pain associated with cervical dystonia. Treatment with the product interrupts cholinergic transmission between the nerve and the affected muscle, causing the muscle to relax.

Myobloc was approved on the basis of results of two multicenter, double-blind, placebo-controlled trials in which the primary efficacy outcome variable was the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) at week four. In the first trial, 109 patients with acceptable response to type A toxin were randomly assigned to receive 10 000 or 5000 units of Myobloc or placebo, injected in two muscles. Their mean improvements from baseline in TWSTRS-total scores were 11.7, 9.3, and 4.3 points on the scale, respectively. In the second trial, 77 patients who had secondarily lost responsiveness to type A toxin were randomly assigned to receive 10 000 units of Myobloc or placebo. Their mean improvements in TWSTRS-total scores were 11.1 and 2.0 points on the scale.